The present embodiments relate to computer networks and are more particularly directed to a bridged network system in which traffic resiliency is provided by quickly switching traffic to a pre-identified route upon a link failure.
A bridged network is one type of network that has found favor in various applications in the networking industry, and for various reasons. A bridged network in many approaches is based on Ethernet switches that are Layer 2 switches, and the basic principle of operation of such a network includes learning of MAC addresses, broadcasting of unknown MAC addresses, and use of a Spanning Tree Protocol to provide loop-free operation. With Ethernet used as a technology in a bridged network, it is a widely used and cost effective medium with numerous interfaces and capable of communications at various speeds up to the Gbps range. With the use of such networks, mechanisms for routing and re-routing traffic have evolved in the instance of a communication failure between bridged network nodes. In this context and throughout this document, the term “node” includes what are referred to in the art as switches or bridges and is known as a device for communicating a block of data. The data block is often referred to as a packet or frame and it is transmitted in the bridged network from one node to another node that is connected to the transmitting node via a physical line referred to as the link and according to a protocol. One common protocol that is particularly used to provide loop-free operation and resilience is the spanning tree protocol, with a specific type of that protocol being known as the rapid spanning tree protocol (“RSTP”). The RSTP provides various aspects, where one is to provide a so-called spanning tree along which data packets pass. The spanning tree is logically defined to include a root node that transmits via logical links to other intermediate nodes and ultimately to an endpoint node. In the spanning tree configuration, if there is a failure along the tree then the RSTP provides communications among the various nodes so as to “re-converge” to a new spanning tree (i.e., a new different set of logical links), and thereafter traffic is routed according to the new spanning tree. Each spanning tree in the prior art has the characteristic that it prevents loops from occurring in response to broadcast transmissions, that is, it breaks what otherwise could be a loop in transmissions and thereby prevents a same node from receiving duplicate packets along different links in the same network.
While the spanning tree protocol has proven beneficial in some implementations, it also may provide certain drawbacks. For example, the RSTP may be relatively slow to re-converge to a new tree following a failure because the protocol relies on exchange of bridge protocol data units (“BPDUs”) between the nodes and the root. Hence, depending on the topology, fast re-convergence may not be possible and the re-convergence times can take up to two to three seconds. For some applications this is not an acceptable figure. Further, during operation under RSTP and in response to a failure, MAC addresses need to be flushed and re-learned which is an expensive operation. Consequently, these approaches are not being viewed as carrier-grade technology.
In view of the above, there arises a need to address the drawbacks of the prior art, as is accomplished by the preferred embodiments described below.